Electrodeposition of copper from fused baths



Patented Apr. 25, 1944 ELECTRODEPOSITION OF COPPER FROM FUSE!) BATIIS James H. Young, Niagara. Falls, N. Y., assignor to E. I. du Pont de Nemours & Company, Wilmington, Dei., a corporation of Delaware No Drawing. Application August 27, 1941, Serial No. 408,492

8 Claims.

This invention relates to electrodeposition of copper and more particularly to the electrodeposition of copper for fused salt baths.

I have discovered that the electrolysis of fused alkali metal cyanide containing from about 1-50%. by weight of copper cyanide dissolved therein results in the efficient electrodeposition of copper at the cathode. I have further found that adherent coatings of copper of good quality can be produced by such electrodeposits on the surface of iron or steel or other base metals by this method. I have further discovered that by suitably modifying the electrodeposition process, spongy deposits of copper can be obtained from which a high grade of copper powder is readily obtained.

Therefore, the objects of the present invention include an improved method of copper electrodeposition, the preparation of dense and adherent coatings of electroplated copper on iron and steel, and other metal bases, and also the production of copper sponge and copper powder by electrodeposition. Further objects of the invention will be apparent from the ensuing description.

To practice my invention I may fuse an alkali metal cyanide, for example, sodium cyanide, po-

best results are obtained when an excess of the alkali metal cyanide is present. In preparing the adherent copper plate it is especially desirable that an excess of sodium cyanide be present. preferably at least two moles for each mole of copper cyanide. A very large excess of the alkali metal cyanide is not deleterious; for example, good results may be obtained with a melt containing 1% by weight of copper cyanide and substantially 99% by weight of sodium cyanide.

To prepare an iron or steel surface for elec--' trodeposition of the above described adherent coating copper the surface may be, pickled and cleaned by methods commonly used in electroplating practice. I prefer, however, to clean the base metal in the above described cyanide electrolyte for the copper plating process heretassium cyanide, or mixtures of such alkali metal cyanides and add thereto solid copper cyanide in an amount equal to about 1-50% by weight of the total melt. The copper cyanide added may be either cuprous or cuprir cyanide. Preferably I add cuprous cyanide, since it generally is more readily available and because the cupric variety apparently is reduced by the alkali cyanide, thus wasting a portion of the latter. The resulting copper containing melt is eiectrolyzed, utilizing direct current and conventional eiectropiating procedures. If it is desired to obtain an adherent, dense coating of copper on the cathode the melt must not contain more than about 5% by weight of copper cyanide, pref erably 1-5% by weight, and the cathode current density must not exceed about'35 amperes per square foot, preferably about 7 to amperes per square foot. If the current density exceeds this figure, the deposit on the cathode becomes semi-adherent, and tends to become spongy or rough and more or less porous. Preferably, the bath temperature should not exceed about 600 C.

Preferably, the relative concentrations of copper and sodium cyanides in the bath are such that there is a least one mole of sodium cyanide for each mole of copper cyanide. In general,

in described. Satisfactory cleaning thus may be obtained by making the article to be plated the anode in my electrolyte and impressing thereon a suitable electric current, for example of a current density of ten to forty amperes per square foot.

In another method of operating my invention I may utilize a melt containing from about 10-50% by weight of copper cyanide whereby an exceedingly spongy electrodeposit of copper is obtained on the cathode. In producing such spongy copper, control of the cathode current density ordinarily is not important except that by use of higher current densities the rate of production is ccrrespondihgly increased. Generally, best results are obtained at bath temperatures not exceeding about 600 C. The electrodepositecl spongy copper for the most part adheres to the cathode rather than falling off into the bath. To recover the sponge copper thus produced, the cathode is removed from the bath. cooled, and washed with water to wash out adherin electrolyte. During this washing operation the sponge copper readily becomes detached from the cathode. The sponge thus produced has a bright metallic luster and a fibrous appearance. It is exceedingly bulky ordinarily having an apparent bulk density in the neighborhood of 5 cc. per gram. Mild mechanical treatment readily disintegrates the sponge to produce a copper powder having substantially the same bulk density as the sponge.

Various modifications and adaptations of the herein described process may be carried out without departing from the spirit and scope of my invention. For example, if desired, various inert fusible inorganic salts may be added to the electrolyte, for example, alkali metal cargenerally is to adjust the melting point of the bath and to utilize less expensive ingredients.

A preferred method for reducing the melting point is to utilize a mixture of alkali metal cyanides, e. g., a mixture of sodium and potassium cyanide, with or without the addition of fusible diluents.

As compared with electroplating copper from aqueous solutions I have discovered that my process is well adapted for the production of copper coatings. I have also found that the dense adherent type of copper coatings produced according to my process appear to be more porous than the adherent copper coatings produced by aqueous electrolysis; and yet my coatings thus produced are free from "pin holes" and afiord protection against corrosion substantially equal to that obtained by plating from aqueous solutions. Coatings thus obtained by my process, being porous, are capable of absorbing. oils, aqueous solutions and other liquids, which property is not shared by adherent electrodeposits from aqueous solutions. I have also discovered that the copper coatings obtained by my process have adherence to underlying iron or steel surfaces equal to that of electrodeposits ordinarily obtained from aqueous solutions, and are more adherent than any known porous copper deposit obtainable by aqueous electrolysis.

A further advantage of my process, as comrelatively lower power consumption. This arises from the high conductivity of the melts and the fact that the copper in the melt is in the monovalent state. Thus I have found, for example, that at a current density of about 100 amperes per square foot a voltage of about 0.3 volt is ample, whereas in aqueous solutions of copper salts commonly employed, voltages of around 2.3 volts are required for this current density.

Iclaim:

1. The process 'for electrodeposition of copper which comprises electrolyzing a molten bath which consists essentially oi alkali meta1 cyanide and about 1 to 50% by weight of copper cyanide, at a temperature not greater than about 600 C.

2. The process for electrodeposition of an adpared with aqueous electrolysis of copper is the herent porous deposit of copper which comprises electrolyzing a molten bath which consists essentially or sodium cyanide and about 1 to 5% by weight of copper cyanide at a temperature not greater than about 600 C. and at a current density or about 7 to 35 amperes per square foot.

3. The process for electrodeposition of an adherent porous deposit of copper which comprises eleotrolyzing a molten mixture consisting essentially of sodium and potassium cyanides and aboutl to 5% by weight of copper cyanide at a temperature not greater than about 600 C. and at a current density 01' about 7 to 35 amperes per square foot.

4. The process for production of electrodeposited copper sponge which comprises electrolyzing a moltencyanide bath which consists essentially of sodium cyanide and about 10 to 50% by weight of. copper cyanide at a temperature not greater than about 600 C.

5. The process for production of electrodeposited copper sponge which comprises electrolyzing a molten mixture consisting essentially of sodium and potassium cyanides and about 10 to 50% by weight of copper cyanide at a temperature not greater than about 600 C.

6. The process for production of electrodeposited copper sponge which comprises electrolyzinga molten alkali metal cyanide bath which contains about 10 to 50% by weight of copper cyanide and at least one mole of alkali metal cyanide for each mole of copper cyanide, at a temperature below the melting point of copper, removing the resulting spongy mass of electrodeposited copper coated with molten bath, cooling it and treating it with water to dissolve and remove adhering bath. I y l 7. The process for production of electrodeposited copper sponge which comprises electrolyzing a molten cyanide bath which consists essentially of sodium cyanide and about 10 to 50% by weight of copper cyanide at a temperature not greater than about 600 C., removing the cathode with spongy copper electrodeposit adhering thereto from said bath and contacting it with water-to remove said electrodeposit and wash cyanide therefrom.

8. The process for production of electrodeposited coppersponge which comprises electrolyzing a molten mixture consisting essentially of sodium and potassium cyanides and about. 10 to 50% by weight of copper cyanide at a temperature not greater than about 600 0., removing the cathode with spongy copper electrodeposit adhering thereto from said bath and immersing it in water to remove said electrodeposit and wash cyanide therefrom.

JAMES H. YOUNG. 

